760 METABOLISM 



things they become so only when they are improperly used when a per- 

 son overheated by being in a hot atmosphere is suddenly subjected to a 

 restricted draft, of course there is danger that the sudden change of 

 conditions, affecting one part of the body only, will cause vascular dis- 

 turbances that may be undesirable, but if the conditions be properly con- 

 trolled, drafts are the healthiest things and the best tonics. 



It is a common experience not only that ordinary colds, but more 

 serious infections as well, can be directly traced to some unsuitable 

 condition of ventilation ; such as sudden exposure to a draft while over- 

 heated, or going out into a cold, damp atmosphere from an overheated 

 room. What is the reason for the infection under these conditions? At 

 the outset we must recognize that all these conditions, colds, catarrhs, 

 bronchitis, just like the more acute infectious diseases, as diphtheria, 

 pneumonia, cerebrospinal fever, etc., are due to microorganisms, and the 

 question therefore is why should unfavorable ventilating conditions so 

 frequently be the immediate cause of the attack. 



There are two methods by which the infection might occur. First, by 

 a great increase in the number of organisms in the air, and secondly by 

 a lowering of the resistance of the body towards the organisms, which 

 would not then require to become increased in numbers. The former 

 method is usually known as mass infection, and there can be no doubt 

 that it is very common, perhaps, indeed, is the commonest cause for 

 infection. The organisms, of course, come from infected individuals, 

 who add them to the atmosphere in the exhaled air, particularly when 

 this is forcibly discharged as in coughing or sneezing, or even in speaking. 



Evidence of the importance of this factor is as follows. If the mouth be rinsed with 

 a culture of some readily recognizable organism not commonly present in detectable 

 amounts in the atmosphere, and the person, standing in front of a row of P'etri dishes 

 each cotaining some culture medium upon which the organism will grow, then speaks at 

 ordinary pitch, the plates after proper incubation develop colonies of the organism, those 

 nearest the speaker having most, but even those at a distance of several feet also show- 

 ing them. 



A serious problem in zoological gardens has been to keep animals that are highly 

 susceptible to tuberculosis free from this disease. The higher apes, for example, inevi- 

 tably succumb to this disease, being infected by the bacilli exhaled by persons standing 

 in front of their cages, many of whom harbor these bacilli, though they may not show 

 any of the symptoms of tuberculosis. Now it has been found that if glass screens are 

 erected in front of the cages, the animals remain almost free from the disease. 



But mass infection does not suffice to explain the cause for the onset 

 of attacks of many conditions that are, nevertheless, fundamentally due 

 to bacteria, such as ordinary colds. These can frequently be traced to 

 some chill, or wet feet, or exposure to sudden change in temperature. In 

 such cases it is believed that the bacteria are present on the mucous mem- 

 branes of the upper respiratory passages, but that they remain inactive 



